The invention relates to a control device for launch assistance for a motor vehicle and to a corresponding method.
During a launch process of a motor vehicle, it is basically possible for an undesired stall of the internal combustion engine to occur if the torque provided by the internal combustion engine is not high enough. Here, the dual-mass flywheel, also referred to as ZMS, is briefly operated in a resonance range. In order to prevent damage to the dual-mass flywheel, so-called protective functions are implemented in the vehicle, which identify a stall of the engine at an early time and initiate corresponding measures to prevent damage to the components. Here, it is basically the case that the rotational speed signal of the engine is measured, and a stall of the engine is detected if the rotational speed of the engine falls below a predefined rotational speed threshold—of e.g. 400 revolutions per minute (rpm).
For example, DE 10 2008 052 839 A1 discloses a control device for a motor vehicle which detects a stall of the engine on the basis of the rotational speed of the engine and, if a stall of the engine is detected, subsequently initiates an automatic start if corresponding conditions are satisfied. In detail, a stall of the engine is detected if the rotational speed falls below a predefined low rotational speed threshold, or if the rotational speed of the engine, proceeding from an initial rotational speed exceedance of a predefined high rotational speed threshold, then undershoots the predefined low rotational speed threshold.
Furthermore, the as yet unpublished DE 10 2015 202 932 A1 discloses a control device for the early identification of the stall of an engine in a motor vehicle, the control device being designed to identify a stall on the basis of the clutch-engagement rotational speed and the rotational speed gradient of the engine rotational speed.
To prevent a stall, DE 10 2011 120 173 A1 discloses a control device of a hybrid vehicle with manual gearbox, wherein a controller of the control device is designed to control the torque output by the engine such that a stall of the engine and/or excessive revving of the engine during a manual actuation of the clutch is prevented. To identify an impending stall situation, the controller receives one or more signals from an input shaft sensor, from the clutch pedal sensor and from the accelerator pedal sensor, and correspondingly evaluates said signals. Such an approach is cumbersome and associated with high costs, because such sensors are not normally installed in the vehicle. Furthermore, this functions only in interaction with an electric machine.
It is now an object of the invention to provide an improved control device and a corresponding method for the early identification of a stall of the engine and for initiation of corresponding countermeasures.
This and other objects are achieved by way of a control device and corresponding method for launch assistance for a motor vehicle having an internal combustion engine as drive engine, which control device is designed to predict a stall of the internal combustion engine of the motor vehicle on the basis of at least one signal, and, if a stall of the internal combustion engine is predicted, to output a signal for initiating launch assistance. The control device is designed to predict a stall of the internal combustion engine on the basis of the engine rotational speed of the internal combustion engine and the gradient of the engine rotational speed of the internal combustion engine before the clutch-engagement rotational speed is reached. And, if a stall of the internal combustion engine is predicted, the control device is configured to output a signal for initiating an increase of the engine torque demand of the internal combustion engine.
The invention is based firstly on the knowledge that, if a stall is identified during launch by evaluation of the rotational speed with regard to an undershooting of a threshold value, the selection of the threshold value constitutes a fundamental problem. If the threshold value is selected to be too high, corresponding protective measures are duly initiated at an early time, but the likelihood of so-called incorrect identification increases, that is to say the corresponding protective measures are initiated more often than required. This would in turn have an adverse effect on customer acceptance. However, if the threshold value is selected to be too low, the rotational speed of the engine may fall into a very low range, even into the resonance rotational speed range of a dual-mass flywheel. This would, at least in the case of certain engine variants, lead to extremely large rotational oscillations in the dual-mass flywheel, which, under some circumstances, would cause irreversible component damage even in the event of a single occurrence.
Taking this knowledge into consideration, it is proposed, with regard to the predictive identification or prediction of an impending stall situation, that a control device for launch assistance for a motor vehicle having an internal combustion engine as drive engine be provided, which control device may be a control unit having a processor and is designed to predict a stall on the basis of the engine rotational speed of the internal combustion engine and the gradient of the engine rotational speed of the internal combustion engine before the clutch-engagement rotational speed or clutch-engagement time is reached. To prevent a stall, the control unit is, according to the invention, furthermore designed such that, if a stall of the internal combustion engine is predicted, said control unit outputs a signal for initiating an increase of the engine torque demand (and thus of the engine torque) of the internal combustion engine.
It has been discovered that, in an advantageous embodiment of the invention, the rotational speed gradient of the internal combustion engine can be determined in a manner dependent on at least a minimum rotational speed of the internal combustion engine during at least one preceding ignition event of the engine before the clutch-engagement rotational speed or the clutch-engagement time is reached, in particular from the minimum rotational speeds of the internal combustion engine of at least two or more ignition events of the internal combustion engine before the clutch-engagement rotational speed is reached. It is likewise possible for the rotational speed gradient of the engine rotational speed to be determined by way of the engine rotational speed at the top dead center of each cylinder and the time between two ignition events.
It is advantageously possible, for the detection of an impending stall of the engine, for consideration to additionally be given to a further signal which provides an indication of an impending stall of the engine, that is to say the control device is advantageously designed to predict a stall of the internal combustion engine, before the clutch-engagement time is reached, on the basis of the engine rotational speed of the internal combustion engine and the gradient of the engine rotational speed of the internal combustion engine and at least one further signal. An evaluation of a signal which corresponds to the rotational speed of the gearbox input shaft is advantageously suitable here.
In a particularly advantageous embodiment of the invention, the control device is designed to predict a stall of the internal combustion engine on the basis of the engine rotational speed of the internal combustion engine and the gradient of the engine rotational speed of the internal combustion engine and the rotational speed of the gearbox input shaft and/or the gradient of the rotational speed of the gearbox input shaft.
To now be able to detect a stall of the internal combustion engine at an early time, that is to say predictively, the control device is advantageously designed to predict a stall of the internal combustion engine on the basis of a calculated clutch-engagement rotational speed, in particular if the clutch-engagement rotational speed, which is calculated on the basis of the engine rotational speed and the gradient of the engine rotational speed, and possibly on the basis of the rotational speed of the gearbox input shaft and/or the gradient of the rotational speed of the gearbox input shaft, is lower than a predefined (variable) clutch-engagement rotational speed threshold.
If, by way of the correspondingly designed control device, a stall of the internal combustion engine (during the launch process) is predicted at an early time, corresponding measures for preventing a stall of the internal combustion engine and for preventing component damage must be implemented. According to the invention, for this purpose the control device is advantageously designed to initiate, if a stall of the internal combustion engine is predicted, a targeted increase of the engine torque and/or of the assumed clutch-engagement rotational speed by initiating an increase of the engine torque demand of the internal combustion engine. For this purpose, the control device is advantageously designed to output, if a stall of the internal combustion engine is predicted, a signal for initiating an increase of the engine torque demand of the internal combustion engine, such that a correspondingly dependent increase of the engine torque demand occurs. The signal is dependent on the calculated clutch-engagement rotational speed or is dependent on (i) the present rotational speed of the internal combustion engine, (ii) the present rotational speed gradient of the internal combustion engine, (iii) the present rotational speed of the gearbox input shaft, and/or (iv) the present rotational speed gradient of the gearbox input shaft. In other words, it is possible for an increase of the engine torque demand to be performed, for example, in a manner dependent on the deviation between the calculated clutch-engagement rotational speed and a required clutch-engagement rotational speed. The magnitude may be predefined in particular in a manner dependent on the magnitude of the deviation.
It is likewise the case, in an advantageous refinement, that the control device is designed to at least partially withdraw a signal for increasing the engine torque demand of the internal combustion engine, which signal has been triggered if a stall of the internal combustion engine is predicted, if a stall of the internal combustion engine is no longer predicted on the basis of a determined calculated clutch-engagement rotational speed.
The above statements with regard to the control device according to the first aspect of the invention correspondingly also apply to a method according to the second aspect of the invention.
The method according to the invention, and the advantageous refinements thereof, may be performed by way of an implemented algorithm or a corresponding component arrangement in a processor-based control unit provided for the purpose, in particular in an engine control unit.
A third aspect of the invention is directed to a vehicle which includes a control device as described above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.